In plasma metal etch processing, (a typical arrangement is shown in FIG. 2), the process chamber 20 is connected by vacuum piping to a vacuum system including: a screen 56, a throttling valve assembly 24, a gate valve 26, a turbo (booster, turbo molecular) vacuum pump 28, and an isolation valve 30 connecting to main vacuum pumps (in the direction of the arrow 32). The throttling valve assembly 24 is generally a butterfly type throttling valve installed in the exhaust gas line between the process chamber 20 and the vacuum pumps. The throttling valve regulates the pressure in the etch process chamber 20. Gases used in the process chamber often produce etch byproducts, e.g., Al.sub.2 Cl.sub.3, polymeric reaction products. These reaction products are drawn into the vacuum piping and rapidly condense on and coat the throttling valve tending to create particulates that have been found to contaminate the wafer in the process chamber.
To maintain chamber particle contamination at acceptable levels the heavy polymer deposits on the throttling valve must be removed. Considerable time (several hours) must be spent removing and cleaning the throttling valve. The throttling valve is an integral part of the process chamber vacuum piping. To remove and clean the throttling valve, the piping adjacent the valve must be disturbed, if not completely disassembled, to permit the throttling valve to be removed. Each removal, cleaning, and reassembly cycle increases the possibility of damaging the piping or the valve and creating a vacuum leak.
The deleterious effect of particulate contamination on the processing chamber and wafer(s) being processed due to polymer buildup is unacceptable. Repeated breach of the vacuum system to remove, clean and reinstall the throttling valve is a very burdensome and time consuming procedure when the piping (pumping stack or pumping system) has to be disturbed or disassembled for each cleaning. It reduces the process chamber throughput (increases production system downtime) and creates a higher risk of component damage.